Pavement



0d 3v 1933 A. H. lRvlNG ET AL 1,929,279 l PAVEMENT Filed Feb. 24. 1931IAWENTOS ANDREW H. few/v OWEN H. ROBERTSON W62@ J @2M THE/E ATTORNEYPatented &3, li933 UNITED STATES PATENT oFFicE PAVEMENT Andrew H.Irving, Berkeley, and Owen.

' Robertson, Paraiiine San Francisco.

Calif., a corporation of Delaware h Application February 24, l1931,.serial No.v517,754 2 Clalmsf (CL 94-5) Our invention relates to apavement, and particularly to improvements in the wear-taking layer of apaving structure which possesses the property of healing over minorinjuries inflicted in its surface, such as that described in the patentto William H. Lowe, No. 1,610,019, patented Dec. 7, 1926.

It is among the objects of our invention to provide a pavement which ispossessed of great durability together with a certain measure ofresilience coupled with vibration absorbing and sound deadeningproperties.

Another object of our invention is the provision, in a pavement of thecharacter described, of a wear-talng layer which presents a skidprooftraction surface.

Another object of our invention is the provision, in a pavement of thecharacter described, of means for reducing the resistance to truck- Afurther object of our invention includesthe provision, in a pavement ofthe character described, of means for accomplishing the above mentionedobjects without imparing the healing properties of the traflic sheet, asset forth in the patent previously referred to.

'I'he invention possessesother objects and features of advantage, someof which, with the foregoing, will be set forth in the followingdescription of our invention. It is to be understood that we do notlimit ourselves to this disclosure of species of our invention, as wemay adopt variant embodiments'thereof within the scope of the claims.

Referring to the drawing:

' The ligure of the drawing is a perspective view showing a portion ofthe pavement embodying our invention. Part ofthe finishing coating is pomitted to show more clearly the character of the wear-taking layersurface.

In connection with paving structures it is difllcult to over-estimatethe value of a trac sheet having a wear-taking layer of viscous materialslightly and slowly owable under pressure to render it capable ofcoalescing after scarring, so that a continuous smooth surface isrestored by wear. Possessed of this self-healing property awear-taking-layer soon lls up and heals over minor mechanical injuriesinflicted by the wearing action of heavy shoes, falling objects,vehicular tralc and other destructive agencies.

When a wear-taking layer of this sort is provided as a coating over abase layer having a certain measure of resilience, such as a brous layersaturated with a semi-solid material, a

trailic sheet is provided which is characterized by extreme durability;in actual tests it having been found that the sheet will outwear asteelplate. Accompanying the advantages that flow from this traffic sheethowever are certain inherent disadvantages.

The first of these is the'fact that the material in the wear-takinglayer tends to ow out under the pressure of a load and hill-up ahead ofa moving truck wheel. The effect of this is to materially increase theresistance to trucking, because a truck is constantly having to climbover a small hill of material. The second disadvantageous feature liesin the fact that the wear' taking layer becomes slippery when wet; thisfactor being accompanied by a decrease in traction and increased dangerto traihc.

The broad object of our invention is to improve a paving structure ofthe general character described by providing a. traffic sheet Ahaving awear-taking layer possessed of the self-healing properties pointed out,which materially reduces the resistance to trucking, and which presentsa skid-proof traction surface.

In terms of broad inclusion, the pavement embodying our inventioncomprises a traffic sheet overlying and preferably united with asupporting substructure. 'Ihe traic sheet comprises a wear-taking layerof viscous material slightly and slowly -ilowable under pressure torender it capable of coalescing after scarring, so that a. continuoussmooth surface is restored by wear. This wear-taking layer is filledwith a stiiening material to prevent the owable material from hilling-upunder a rolling load, and without impairing the surface restoringproperties of the layer.

' The filling material is preferably of a granular nature, such as sand;it having been found that such material preserves the self-healing.properties of the wear-taking layer, and at the same time materiallyreduces its resistance to trucking. Furthermore,V the granular filledlayer presents a non-skid traction surface. The viscous material of thewear-taking layer is preferably a bituminous material solid atordinary'temperatures but capable of coalescing after scarring, and ispreferably applied as a coating on a preferably resilient base layer.This base layer is preferably a brous layer saturated with a semi-solidmaterial. The base layer and wear-taking layer form an integral mass,and this trafic sheet is preferably adhesively united with thesupporting substructure, so that a` unitary paving structure isprovided. 110

In greater detail, the preferred form of pavement embodying theimprovements of our 'invention comprises a traffic sheet overlying andpreferably united with a supporting substructure, such as the concretefoundation 2. The bond between the traffic sheet and substructure ispreferably secured by a layer 3 of adhesive, such as a bituminouscement. A relatively hard steam blown asphalt dissolved in carbonbisulfide,

benzole, or other suitable solvent may be used inA The furnish for thisfelt may be of any suitable material, such as for example a furnishcomprising 10% old newspapers, 15% wool rags, 10%

burlap and 65% cotton rags. If desirable, a filler, such as wood sawdustor the like, may be added to the furnish. The stock is preferably beatenvery short, for such a weight of felt, and is preferably well jordaned.

In order to give body and strength to the brous layer, and at the sametime render it waterproof and protect it against deterioration, the baselayer is preferably treated with a suitablesaturant. Furthermore, inorder to give the treated fibrous layer a certain measure of resilience,the

f base layer is preferably saturated with a semisolid material. Abituminous saturating compound, such as a good grade of soft blownasphalt having a softening point of from ,120 to 125 and a penetrationof from 5,0 to 80, according to the standards-of the American Societyfor Testing Materials, has been found to characterize the fibrous layerwith the desired properties, and is preferably employed.

A wear-taking layer 6 of viscous material is provided, and is preferablyapplied as a coating -nbrous layer to over the base layer 4. Theconsistency of this viscous material is such that it is slightly andslowly flowable under pressure to render it capable of coalescing afterscarring, so that a continuous smooth surface is restored by wear. Abituminous compound, s'uch as a blown California asphalt having asoftening point of from 180 to 195 and a penetration of from 12 to 18,also according to the standards of the Society for Testing Materials, ispossessed of the desired characteristics, and is preferably used for thecoating 6. This coating layer, while solid at ordinary temperatures, iscapable of slow flow under pressure, so that the viscous material willcoalesce after scarring to restore a uniform smooth surface under theaction of continued wear.

We have found that a s 'table weight for the coating 6 is about 13 lbs.per 100 square feet of coated area, thisweight however may be varied tosuit a given set of conditions. If desirable, a coating of this materialmay be applied to the underside of the treated brous layer 4 for addedprotection. This c oating of course may conveniently be made lighterthan the upper coating 6; a weight of 9 lbs. per 100 square feet ofcoated area having been found suitable. The coatings 6 and 'l unite moreor less with the saturant of the provide a traino sheet of integralmass, and, since the cementing compound of the bonding layer 3 unitesthe protective layer '7 with the foundation 2, a unitary pavingstructure is provided. This unitary construction of the pavementprevents lateral slipping of the trame sheet and narrowly localizesshocks and stresses.

While the pavement as above described is satisfactory, and itself is farin advance iny point of resistance to wear as compared with othertypesof pavements, it has a tendency to offerresistance to vehiculartramc,`and to become slippery when wet. The reasons underlying the firstmentioned of these tendencies are not obvious, but

' the presence of a resistance to trucking is none the less certain astraction tests have proven.

It is believed however that the resistance is due to a flowing out ofthe viscous material under the pressure of a truck wheel, and ahilling-up of this material ahead of 'the wheel as it progresses alongthe surface of the wear-taking layer; the effect being that the truck isconstantly having to climb over a small hill in the surface of thelayer. In order to overcome this hillingup tendency, and still notimpair the healing" or surface restoring properties of the wear-takinglayer, we have filled the layer 6 with a stiffening material 8. Thismaterial is preferably a granular material, such as sand.

By using a sand filled coating, formed from a mixture of 60% asphalt and40% sand, we have found by actual traction tests that the resistance toa rolling load is much less as compared with a non-filled coating. Thestarting resistance in 105 both cases is about the same, but, since theperiods of starting are very short as compared to the periods ofrolling, this fact is of little conse- -quence in practical truckingoperations. Furthermore, actual tests show that the sand filling in thecoating does not impair its self-healing properties,` and while the sandmight operate in a minor degree to oppose this action, the opposition isnot sufilcient to be noted in tests under practical conditions. I

It is believed that the filling of granular material hardens, or moreprobably toughens, the viscous material sufficiently to prevent thehillingup yprocess when a load is rolling. At the same time, the amountof filling material in the coating necessary to accomplish this resultis not sumcient to impair .its healing properties. The sand used in thecoating is preferably a hard silica sand of a size which will passthruja 30 mesh screen and be retained on a 50 mesh screen. It 125 is tobe understood however that the nature and Ysize. of the granularmaterial, as well as the amount used in the coating, may be varied; vtheabove mentioned specification for this material being set forth merelyas an example. 13,()

The granular filling material in the wear-taking layer also provides askid-proof traction surface, which not only greatly increases tractionwhen the surface of the layer becomes wet, but also materially enhancesthe safetyto vehicular traffic. It is believed that the function of thegranular material in this respect will be understood without furthercomment. If desirable, the wear-taking layer may also be given a dustingof finely ground material 9, such las a ground silica sand of a sizewhich passes thru an 80 or 100 mesh screen, and from which some of thedust has beenvremoved. This finishing coating presents a surface whichis mildly gritty, say like Double 0 sand paper.

In conclusion it is pointed out that a pavement is provided which iswaterproof and decay-proof; which is highly resistant to wear; which ischaracterized by a certain measure of resilience to render it vibrationabsorbent and sound deaden- Mq,

structure of represents a skidwith a slightly capable o! coalescingafter scarring so that acontinuous surface is restored by wear, theweartaking layer being lled throughout with a granular stitreningmaterial to prevent the owable material from hilling-up under a rollingload without impairing the .surface restoring propl ertiea o! the layer.

2. A pavement comprising a supportingsubstructure. and a traffic sheetoverlying and adhesively ing a fibrous layer saturated with a semi-solidbituminous material to render the tramc sheet slightly and slowlyyieldable under impact, said fibrous layer being coated on` its uppersurface with a bituminous material to form a wear-taking layer solid atordinary temperatures. but capable of coalescing after scarring, thewear-taking layer being lled throughout with sand to prevent the owablematerial from hilling up under a rolling load without impairing thesurface restoring properties of the layer..

. ANDREW H.- IRVING.

OWEN H. ROBERTSON.

" 1miv united to the substructure and compris-V 11s y i

